During surface grinding, a machine tool which commonly includes an electric motor and a grinding disc is usually used. The grinding disc holds mating sandpaper at the bottom thereof. The electric motor drives the grinding disc rotating at a high speed to allow the sandpaper to grind the surface of a targeted object.
During grinding at high speed, dust is generated. Hence the machine tool usually has a hood located above the grinding disc to connect to a suction device to expel the generated dust. For instance, U.S. publication No. 2005/0202769 discloses an improved grinding disc for grinders. It has the grinding disc coupled with a dust suction hood, and an outer wall to form a contact surface with a plurality of axial air vents and a plurality of radial air vents communicating with the axial air vents. The grinding disc is held in a housing chamber of the tool body. The housing chamber has a driving shaft fastened by a fastening portion of the grinding disc. The driving shaft drives the grinding disc to perform grinding operation. Debris and dust generated during the grinding operation are quickly sucked by the air vents on the grinding disc surface and expelled.
However, when the aforesaid machine tool performs larger surface grinding (such as tabletop, wall surface, ground surface and the like), a great amount of dust is generated during high speed grinding. The aforesaid air vents do not have sufficient dust expelling capacity to expel so large amount of dust. A large-scale dust suction apparatus has to be used to suck away the dust, and the air vents could even be possibly clogged. There is still room for improvement.